Ammonia two-phase flow patterns and condensation in the inclined smooth tubes

The paper reports the experimental study of the two-phase ammonia flow patterns and condensation in the upward and downward inclined tubes. The two-phase patterns have been studied by the photography method in the transparent quartz tube of ID 7.5 mm at the inclination of -90 to 90 degrees, saturation temperature of 35-65 degrees C, mass velocity of 40-160 kg m- 2 s-1 and vapour quality of 0.1-0.8. The Hewitt and Roberts (1969) [19] upward pattern map in interfacial momentum flux coordinates compiled for the high-pressure steam water flows was compared with the obtained ammonia patterns, showing satisfactory qualitative correspondence. However, the transition lines quantitatively are not accurate for ammonia, especially in churn-to-slug cases. Matching the twophase patterns and ammonia condensation HTC identified in the prior study for the smooth tubes of ID 8 and 11 mm, a so-called forced convective condensation (flow velocity dependent) domination line has been clearly shown for the upward and downward flows. This line splits the boundary conditions, providing similar condensation HTC for the horizontal and upward/downward flows independently on the expected pattern and with the essentially reduced HTC at the upward/downward configuration. The existence of the HTC maximum for the ammonia flow at the inclination of -30 degrees was proved and quantified experimentally for the broad range of boundary conditions in the ID 8 and 11 mm tubes. Matching the identified condensation HTC and the observed flow patterns allows us to conclude that the condensation HTC maximum is mainly determined by the change of stratified-wavy pattern on a smooth stratified one.